Polarizing materials, such as those used for measuring relative humidity, can be thought of as a resistive element and a capacitive element operatively-coupled in series. Determining the resistance of the polarizing material requires applying a voltage, which will partially add charge to a capacitive element. This polarization may be carried over to the subsequent measurements, making subsequent measurements inaccurate.
Conventional methods of measuring the resistance of polarizing materials have used alternating current (AC). With an AC methodology, polarization built up in the capacitive element during the positive portion of the cycle is undone by polarization of an opposite sign, occurring during the negative portion of the cycle. As a result, the effect of polarization is not fully seen because, when the AC waveform is integrated over a cycle or period, the net voltage is equal to zero. Using AC to measure the resistance of polarizing materials, however, requires electronics that are not commonly integrated into a microprocessor. Furthermore, AC methods are relatively slow because both the positive and negative portions of the cycle are used.
As an alternative to AC methods, a voltage divider can be used to provide pulsed measurement of the polarizing material. Pulse measurement, typically, only makes use of the positive reference cycle of the cycle. A voltage divider, however, is useful only if the time between measurements is substantially greater than the pulse width. When the time between measurements is substantially greater than the pulse width, polarization remaining in the capacitive element will have time to bleed off through the resistor in the voltage divider. However, when time between measurements is not sufficiently large, some residual polarization may remain. As a result, currently, pulsed measurement of polarizing materials is effective only if the material polarizes weakly enough so that the polarization in the capacitive element bleeds off completely between subsequent measurements.
It would be desirable to provide a system and a method for measuring the resistance of polarizing materials, including heavily-polarized materials, using pulsed excitation. Moreover, it would be desirable to provide a system and a method for measuring the resistance of polarizing materials wherein, after the pulse is removed, residual polarization in the capacitive element is removed by shorting the polarizing material.